Starting Monday, a new test that can detect Down syndrome by screening a sample of fetal DNA fragments in the mother’s blood will be on the market in 20 major cities. The test, called MaterniT21, is made by the biotech company Sequenom, and a study published in Genetics in Medicine showed that it has a successful detection rate of 98.6 percent, and a false positive rate of 0.2 percent. MaterniT21 has not been approved by FDA yet (however, the FDA does not typically approve tests only offered by a single lab).

Compared to the invasive amniocentesis and chorionic villus sampling tests that are now used to detect Down syndrome (which have a false positive rate of 5 percent, and carry a slight risk of causing a miscarriage), a simple blood test to detect Down syndrome seems like a good thing. But some people are concerned the test, which is done as early as 10 weeks into a pregnancy, can lead to abortions of affected fetuses. The MaterniT21 test is also not as comprehensive as an amniocentesis or CVS; Down syndrome accounts for only 50 percent of the genetic abnormalities the two traditional tests look for, whereas MaterniT21 only tests for Down syndrome.